1. Technical Field
The present invention relates to photovoltaic devices, and more particularly to inter-digitated contact structures which increase efficiency.
2. Description of the Related Art
Inter-digitated back-contact (IBC) solar cell structures are of interest for increasing the short circuit current (Jsc) (and therefore efficiency) of the solar cells by forming both an emitter and back-surface-field (BSF) contacts on a backside of the solar cell. This permits sunlight to enter from a front side with minimum shadowing loss. In heterojunction solar cells, the emitter stack may be comprised of hydrogenated amorphous Si (a-Si:H) at the front side of the cells, whereas the emitter in homojunction solar cells is comprised of crystalline Si.
IBC heterojunction solar cells need to include a patterned emitter, and BSF amorphous Si stacks need to be properly aligned. This increases the complexity of fabrication and therefore the manufacturing cost. In addition, if lithography is employed for patterning a first stack, removal of residues resulting from the lithography, etching and/or removing the plasma etch damage to a substrate surface prior to the deposition of a second stack is difficult without damage to the first stack. Therefore the use of lithography and etching can compromise an interface between the substrate and the second stack, and as a result compromise the solar cell performance. Moreover, patterning of the second stack without damaging the first stack is difficult because dry or wet etch processes used for etching the second stack can generally etch the first stack at comparable etch rates.